Atmospheric pollution (ozone, aerosols and their precursors) in the Arctic originates primarily from mid-latitude emission regions but also has local sources which are likely to increase in the future due to global warming and economic drivers. It is important to quantify their impacts on regional air quality and climate.

The contribution of different sources to Arctic pollution still remains uncertain despite significant advances, in particular, as a result of field campaigns which took place during the International Polar Year in 2008 (e.g. POLARCAT-France, ARCTAS, ISDAC), and subsequent analysis/data collection that is still on-going (e.g. ANR-CLIMSLIP - http://www.latmos.ipsl.fr/index.php/fr/tact/themes-de-recherche/climslip, LIA YAK-AEROSIB, https://yak-aerosib.lsce.ipsl.fr/doku.php ) involving groups from several laboratories (LATMOS, LaMP, LSCE, LGGE, LMD). Local anthropogenic emissions in the Arctic may be playing a more significant role (direct and indirect effects) than previously appreciated, and are likely to increase substantially in the near to mid-term future. Changing natural aerosols as well as methane also need to be taken into consideration.

With this in mind, we have identified 2 research areas which we feel merit further discussion in the French community as part of the Chantier Arctique prospective:

Local Arctic Pollution: Given the very rapid nature of climate change in the Arctic and global economic pressures, accelerated industrialization in the Arctic is already underway with summer maritime sea routes along the Northern Sea Route already open, and strong interest in oil/gas and mineral exploration in Alaska, Greenland and northern Eurasia. Construction of polar class ships, which can penetrate summer sea-ice across the North Pole, has already been evoked. Local emissions already appear to be influencing atmospheric composition and climate in the Arctic (e.g. flaring and domestic combustion emissions of black carbon in Eurasia, cruise shipping in Svalbard). Significant growth in local sources, together with increased growth in infrastructure, industrialization and/or urbanization, are likely to impact concentrations of trace gases and aerosols and thus, regional air quality and/or climate.

Given the significant uncertainties which exist in quantifying current and future emissions from shipping, oil/gas extraction, metal smelting, mining, domestic combustion as well as boreal/agricultural fires in the Arctic, a combination of local-scale and regional modelling, analysis of existing data (e.g. from EU ACCESS project (www.access-eu.org), ground-based, satellite) and new field data is needed. In particular, an aircraft campaign, using an aircraft from the French fleet, could be used to improve quantification of local emissions and regional budgets. The aircraft, equipped with a full aerosol and trace gas payload, could be based in, for example, northern Scandinavia/ Spitzbergen. It will also be important to take into consideration unique Arctic photochemistry, such as the presence of halogens or snow emissions, which can influence the Arctic oxidising capacity, particularly in the boundary layer where local emissions are occurring. An aircraft equipped with remote sensing instruments (radar and lidar) could also be used for aerosol and cloud studies. A campaign with the Russian YAK aircraft could also be dedicated to these issues since some of the largest uncertainties surround local emissions in Siberia and northern Russia (e.g. fires, smelting, flaring, domestic emissions). New data would be used to improve the representation of emissions and aerosol/trace gas processing in regional/global models as well as to improve emission inventories used for predicting future composition and climate. These data will also help to better understand the impact of pollution on clouds and radiative processes.

Air Pollution Sources in the High Arctic: Significant changes are currently underway in the Arctic Ocean, in particular, the decline of the summer sea-ice with significant reductions in volumes/extend reported. The role of pollutants, and in particular aerosols, in Arctic warming is currently poorly quantified due to a lack of knowledge about important processes and their treatment in models. In particular, there is a lack of information about the vertical distribution of trace gases, aerosols and their speciation as well as cloud microphysics in the high Arctic (>75N) with previous airborne campaigns focusing largely on more southerly Arctic latitudes. Cloud properties related to pollution aerosols are also poorly quantified and new field experiments would benefit from up to date microphysical and remote sensing airborne measurements recently developed in France. A combination of airborne radar/lidar measurements could be used to document aerosols and mixed-phase clouds. Satellite data (e.g. CALIPSO-CloudSat, EarthCare, IASI, GOSAT) can provide additional information (up to 82N for CALIPSO), including regions of pollutant import, but further work is required on retrievals at high latitudes. New developments, as part of the Equipex IAOOS project (http://www.iaoos-equipex.upmc.fr/, 2011-2019), are also underway such as the addition of aerosol micro-lidars to ocean-atmosphere buoys that will be deployed in the Arctic Ocean from 2014/15 and can provide contextual information about cloud/aerosol distributions. Other new approaches could also be envisaged, such as the use of unmanned aerial vehicles (UAVs), as well as the development of new airborne sensors.

A combined approach, based on new field measurements, regional/global modelling and analysis of satellite data, is needed to improve our understanding about the role of pollutants (aerosols, ozone) and feedback processes in the high Arctic. An aircraft campaign using the French aircraft fleet, based in Spitzbergen or Greenland, for example, could be used to collect data on vertical distributions over the Arctic Ocean, in the vicinity of pollutant import regions linking to the IAOOS buoy network and to validate satellite data. The data would be used to improve our understanding about radiative effects and impacts on clouds, and the treatment of such processes in models leading to improved climate predictions. Such an initiative could also contribute to international plans under development as part of the International Polar Initiative (IPI) (http://internationalpolarinitiative.org/) focusing on improving seasonal and climate predictability in the Arctic.

We look forward to discussing these ideas in the French community and welcome any comments or feedback.

Several recent studies havehighlighted that the Arctic is warming twice as fast as the rest of the Earth. Thishas resulted in the shrinking of the Arctic ice sheet and thereby opening upnew shipping channels that were not previously available. The increase in shippingchannels and the consequent urbanization resultsin an increase in local emissions that can have important implications onaerosol properties and their interactions with clouds (liquid and ice phase). It is thought that aerosoldirect (absorption by black carbon) and indirect (aerosol cloud interactions) effectsare likely to play a large role in the rapidly changing Arctic climate. Inaddition to local sources,polluted air masses are transported over long-distancesthat lead to the formation of the Arctic Haze, containing high concentrationsof absorbing aerosol particles.

Predictions of climate warmingin the Arctic from models are considerably lower than observations, therebyhighlighting the need to carry out experiments dedicated to understanding the influenceof anthropogenic emissions in the Arctic environment, and how these emissionsaffect the interactions between aerosol particles and clouds. Although there arean increasing number of ground-based studies, few aircraft observation studieshave performed detailed chemistry measurement of aerosol particles in the Arctic.Aircraft studies are one of the most efficient methods to characterize theinfluence of different air-masses and local sources on the Arctic environment,characterising the evolution of aerosol particles as they leave the source andmix with background air-masses. In addition, they provide a means tocharacterize the vertical profile of the chemical and physical properties ofboth gas and aerosol particles.

The LaMP has three airborneracks that are equipped with a suite of ATR-42 (SAFIRE) certifiedinstrumentation including the C-ToF-AMS (particle chemistry), SMPS and CPC(size distribution measurements), volatility measurements, and impactor stagesfor offline analysis with electron microscopy. This combination of instrumentsallows us to characterize the chemical and physical properties of aerosolparticles with timescales of less than 1 minute. The combination of CPCs andSMPS provides us with aerosol particle number concentration of aerosol particlesas small as 5 nm, providing important information on new particle formationevents (NPF). NPF events (nucleation) can contribute up to 50% to cloud condensationnuclei in the atmosphere, making it essential to characterize the meteorologicalconditions under which they form. Electron microscopy can provide detailedinformation on aerosol composition, morphology, and mixing state which isessential to understand aerosol cloud interactions, and is especially useful inunderstanding the formation of ice crystals.

In addition to airbornemeasurements, ground based in-situ measurements of aerosol particle chemicaland physical properties, together with cloud condensation nuclei measurements canprovide a means to carry out extended studies using additional instrumentation thatcan not be airborne. This extended set-up will allow for process studies in thevery specific conditions of the arctic environment. In particular, shipemissions containing high content of sulfur can lead to large numbers of new particles,that in turn may influence cloud optical properties.

Atmospheric black carbon and ozone precursors typically released by human activities at mid-latitude industrialized regions of the Northern Hemisphere are quickly moved over long distances by atmospheric transport and can reach the Arctic. Black carbon, tropospheric ozone and several other species has become of increasing concern because they can change atmospheric chemistry and air quality in the Arctic and change the radiate balance of the Arctic area. In addition, emissions from forest fires in Siberia and by prescribed agricultural fires in Southern Siberia, Kazakhstan and Ukraine in spring and summer are large sources of trace gases such as aerosols and gas pollutants to the Arctic. YAK-AEROSIB (https://yak-aerosib.lsce.ipsl.fr) aims at tackling these issues by organizing new aircraft campaigns to better document these phenomena and better understand influences on Arctic radiative balance. Aircraft can reach the intercontinental pathways and source areas in Siberia and the Arctic ocean coastal environment. Currently the aircraft is equipped to measure CO, O3, CO2, CH4, and has limited observation capacity for BC and aerosol size distribution. Future campaigns should have an enhanced instrumental package 1- to better resolve the vertical structure of aerosols2- to better observe O3 precursors transport, NOy including NOx and reservoir species (PAN), and 3- to better characterize concentrations, size distribution, chemical and optical properties of aerosols, especially black carbon and organic carbon.Regarding point 1 a microLIDAR is being prepared for following campaigns. Points 2 and 3 would require new in-situ instrumentation. This would possibly include SP2 for black carbon, and an AMS for a better characterization of aerosol size and chemical composition. Few observation techniques detailing total reactive nitrogen are available for aircraft, but chemiluminescence type analysers could be flown to have access to NOx and NOy and possibly CIMS for PAN.